Experience and research have shown that radio and television interference from power lines is mostly caused by arcing ocurring in power line components such as conductor or insulator connections, or other hardware connections. The most troublesome and relatively numerous arcs are the transient arcs or "sparks. " These are very small arcs where the arcing gap is usually less than 0.01" across. Sparks then occur where supposedly mating metal-to-metal surfaces are slightly separated by corrosion and/or looseness and these components are in the leakage path of one phase conductor to ground or such conductor to another phase conductor, resulting in a voltage difference between the separated components.
There are numerous possible sites on a power pole or structure where sparking can occur, and such sparking can cause serious television and radio interference, particularly in weak reception areas.
I have found that in the course of making an interference investigation, it is very helpful to have a noise test source of some type readily available to occasionally check the operating condition of my locating equipment.
In explaining the operation of my locating equipment to others it is most convenient to have a portable sparking source at hand to demonstrate the sensitivity and directivity of my equipment.
In discussing power line interference at a complainant's residence it is effective to be able to demonstrate how electrical interference appears on a TV set or sounds on a radio set.
Rather frequently when the investigator of a television or radio complaint first visits the complainant, he finds that no interference is present at the time, because of the intermittent nature of many sources. Then, assuming a TVI complaint, the visit is meaningful if he can use his portable noise source to simulate electrical interference. The complainant can then observe the pattern of this interference on his TV and reply with "yes that's what it looks like," or "that's it all right, but its never quite that bad," or some similar statement. The complainant is assured that the investigator is knowledgeable on the subject of interference and that he knows what to look for in his investigation.
If some strong and some weak TV stations are being received, the investigator may then, with his portable noise source, demonstrate the effects of signal-to-noise ratio on a TV set; that is, demonstrate how much easier it is to interfere with a weak station than a strong; and explain why it is important to have a good antenna pointing in the right direction to increase signal strength to the set to reduce the effects of outside interference.
He may also impress the complainant that if he, the investigator, can so readily cause what looks like power line interference with his portable noise device, the problem might also be some other electrical device in the complainant's home.
For example, on his first visit with the complainant, the investigator may find no interference but be advised that it almost always comes on at about 7 PM. Returning then at about that time he finds it to come on at 7:10 PM; he then isolates the problem to a sparking hot water heater thermostat. This is an easy one, and--assuming in this case the investigator to be a power company employee--the complainant becomes a pleased customer of the power company.
Most often, however, if the complaint is made to the power company, the interference is found to be the result of power line problems. Frequently, of course, interference is intermittent and it may not be "on" when the first visit is made.
Some of the locating instruments in use have a very low inherent background noise output, and the operator cannot always be sure that the instrument used is "on" and in sensitive operating condition. Here the said invention is a helpful aid.
A noise source that simulates electrical noise or interference is very helpful in a classroom situation where power line interference is being discussed, or in a sales presentation where location equipment is being promoted.
Lecture or sales persons have in the past used old "Ford spark coils," neon sign transformers, or ignition or fence charger transformers with spark plugs or other type gaps to simulate power line interference. These are effective but are bulky and inconvenient to set up and also generate a higher level of noise than is required for the demonstration. Further, the use of such transformers may present a safety hazard.
For a discussion of power line and electrical interference, and a discussion of interference locating methods see:
"The Location, Correction and Prevention of RI and TVI Sources from Overhead Power Lines" an IEEE Tutorial publication 76CH1163-5-PWR, July 1976.
For a discussion of interference locators, see my U.S. Pat. No. 4,439,723. See also U.S. Pat. No. 3,820,018.